The invention is based on an impact signaling system for a high-voltage protective device having a housing, having a spring which is arranged in the housing and has a moveable end, having an actuator which can be passed out of the housing and interacts with the moveable end, having a high-resistance resistor wire which is connected in parallel with a fusion wire of the protective device, and having a holder which absorbs the prestress of the spring and can be raised with the aid of an activator above a limit temperature with the load on the spring at the same time being relieved, wherein the holder contains a section of the high-resistance resistor wire which is in the form of a winding and is passed at least once around the moveable end of the spring in order to form the prestress. An impact signaling system such as this has various functions. First of all, the system ensures that a signal is produced in some way, be this optical, acoustic and/or electrical, that the high-voltage protective device has tripped as a result of the currents D passing through the protective device and/or the prevailing ambient temperature. Secondly, the system can also be used in a circuit with a switch/protective device combination to interrupt the current flowing in the circuit, by tripping the switch. In this case, the expression high voltage means rated voltages of more than 1 kV, but in particular rated voltages up to approximately 100 kV. The invention also relates to a high-voltage protective device with this impact signaling system, and to a switch/protective device system with this protective device.
In the introduction, the invention refers to a prior art of impact signaling systems as is described in the Company Document HTBxe2x80x9411/97 xe2x80x9cHH-Sicherungseinsxc3xa4tze mit Temperaturbegrenzerxe2x80x9d [HV HRC fuse links with a temperature limiter] from SIBA Sicherungen-Bau GmbH, Borker Strasse 22, D-44534 Lunen. One impact signaling system which is described in this publication is used in protective devices for medium-voltage switchgear assemblies, that is to say at rated voltages of typically 10, 20 or 30 kV, and has a cylindrical symmetrical housing in which a prestressed helical spring and a pin (which is guided in the interior of the helical spring, absorbs the prestress and is composed of thermoplastic material) are arranged. One end of the prestressed spring, which points upward, is supported on a lower end of the impact signaling device which is in the form of a bolt, and its upper end is passed out of the housing. A high-resistance resistor wire which is connected in parallel with a fusible wire of the protective device is passed in a thermally conductive manner around the housing. The thermoplastic pin acts as a fusible activator which melts above a predetermined limit temperature and in the process reduces the load on the spring and hence trips the impact signaling device. The fusible activator can be activated firstly by the temperature in the protective device being raised above the limit temperature by influences within the protective device, such as long-lasting overcurrents, or external influences, such as heat being supplied from the switchgear assembly or by radiation. Secondly the fusible activator can also be activated when, at a time when the current flowing in the protective device is being limited, the current which is commutated from the low-resistance fusible wire of the protective device into the high-resistance resistor wire heats the fusible activator quickly to the limit temperature.
The activator which causes the abovementioned impact signaling system to be activated is composed of thermoplastic material. However, in general, a thermoplastic has a very wide temperature range in which the strength characteristics of the material are relieved gradually, first of all by softening and later by crystallite melting. It is thus impossible to reliably preclude a wide scatter in the behavior when this impact signaling system trips.
The invention, as it is defined in the patent claims, achieves the object of specifying an impact signaling system of the type mentioned initially which, using simple means, allows a high-voltage protective device to trip reliably in a relatively narrow temperature range.
In the impact signaling system according to the invention, the prestressing force of the spring is absorbed by a section of the high-resistance resistor wire which is in the form of a winding and is passed at least once around the moveable end of the spring, forming the prestress, and which is at least partially in thermally conductive contact with the material of the activator. These measures considerably reduce any scatter in the tripping of the impact signaling system, since the activator now no longer needs to apply the holding force for the prestressed spring, and the holding force now just has to be overcome by removal of the wire winding. Since these two functions are decoupled in the subject matter of the invention, the activator need now no longer have a strength which is sufficiently large to fix the prestressed spring. The activator may thus be composed, irrespective of its strength, of a material which carries out a phase transition, which results in the cancelation of the holding force of the prestressed spring, in a narrow temperature range. This results in the impact signaling system being tripped in a manner subject to only a small amount of scatter, using simple means.
If the activator has a high-energy material with an amount of energy which can be released above the limit temperature which is sufficient to melt the wire winding, then a limit temperature can be achieved which generally fluctuates by approximately xc2x110xc2x0 C. The impact signaling system provided with such an activator according to the invention then has a correspondingly narrow scatter width. Particularly suitable high-energy materials contain a combustible material in particular such as a guanidine or a guanidine derivative, an oxidant which reacts with the combustible material on reaching the limit temperature releasing, in particular such as a nitrate, chlorate, perchlorate and/or permanganate, and possibly a binding agent, in particular such as a paraffin or a polymer. These high-energy materials are described in DE 100 22 41 A1.
A particularly simple impact signaling system is achieved if the activator mechanically fixes the wire winding. Once the activator has been tripped, the point fixing is overcome, and the turns of the winding are open, with the load on the spring at the same time being relieved. The activator is in the form of a point, and fixes the wire winding on the spring, in a manner which is particularly advantageous for mass production. If the activator contains an alloy which melts at the limit temperature, in particular based on silver, copper and/or aluminum, doped with indium and/or germanium, then the impact signaling system according to the invention has a particularly narrow tripping scatter width since the fusion temperature fluctuates only by a few xc2x0 C. Furthermore, the fusion temperature of the alloy and hence the tripping characteristic of the impact signaling system can be varied in a simple manner by varying the doping ratios. Suitable alloys are described in the abovementioned De 100 22 241 A1.
The impact signaling system according to the invention is particularly compact if the spring is in the form of a helical spring and is supported on the housing by a fixed end which is arranged opposite the moveable end, and if the prestress is absorbed by the wire winding which is passed around the moveable end and the fixed end of the spring.